The smell of danger: chemical recognition of fish predators by the invasive crayfish Procambarus clarkii

1. Since avoiding predation can compromise animal fitness, prey are expected to respond to different predator species with an intensity appropriate to the level of risk. In fresh waters, the threat of predation is typically assessed by chemical cues, in particular by odours released by either injured/disturbed conspecifics (conspecific alarm odour) or predators (predator odours). Here, we used the most widely distributed crayfish in the world, the invasive North American Procambarus clarkii, to investigate the relative effectiveness of odours emitted by fish predators compared with conspecific alarm odour. We also tested whether P. clarkii is able to discriminate between fish predators of which it has ‘experience’ (either recent, via introduction to the same water body, or old, by sharing a native range), as well as between fish predators that pose low or high risk. 2. The study was carried out on introduced populations of P. clarkii from two sites, characterised by different fish assemblages: the Malewa River (a tributary of Lake Naivasha, Kenya) and Lake Trasimeno (Italy). Laboratory experiments consisted of three sequential phases (‘water’, ‘food’ and ‘smell’ phases) and five treatments. Treatments differed in the odour presented during the smell phase, i.e. no odour (plain water) and odours from either injured conspecifics or three fish species per site. Crayfish from the Malewa River population were confronted with the odours of largemouth bass (Micropterus salmoides), common carp (Cyprinus carpio) and tilapia (Tilapia zillii) (all introduced to Lake Naivasha but absent from the Malewa River), and those from the Lake Trasimeno population with the odours of the introduced largemouth bass and carp and the native chub (Squalius cephalus). Largemouth bass is the only predator that imposes a high risk to crayfish, and it also shares its native range with P. clarkii. We analysed the time spent by crayfish feeding, in locomotion and in adopting a raised or lowered posture. A reduction in the time spent feeding and in locomotion, and an increase in the time spent in the lowered posture were considered to indicate alarm. 3. Crayfish from both populations responded with a more pronounced reduction in feeding to conspecific alarm odour rather than to predator odours. Crayfish from the Malewa River reacted with the same intensity to the odours of the three fish species tested, whereas, in Lake Trasimeno, the odour of largemouth bass was significantly more threatening than the odours of the other two species. 4. Procambarus clarkii seems to perceive a general fish odour that alerts it to possible predation risk without the need of either a direct recent experience or via sharing a common native range. However, where they coexist with fish, crayfish become able to distinguish among species, adapting the intensity of their response to the effective risk. Our results confirm the relatively high learning capacity of P. clarkii reported in previous studies and suggest the existence of mechanisms that make predator recognition particularly efficient in this extraordinarily successful invader.     

Growth and reproduction in the freshwater crab, Potamon fluviatile (Decapoda, Brachyura)

SUMMARY. 1. The patterns of relative and absolute growth and the reproductive biology of the freshwater crab Potamon fluviatile were studied in a natural population inhabiting a hill stream close to Florence, Italy, over an annual cycle. Periodical inspections of a stretch of the stream were made and morphological and anatomical analysis carried out.
2. As in other decapods, the females are smaller than the males (they can however occasionally reach larger dimensions). This may be determined by a lengthening of the moulting interval in the females, by their higher energetic cost of reproduction (since reproduction occurs simultaneously with moulting, at least in this habitat) and/or by a higher mortality rate resulting from the risks associated with carrying eggs and vagility.
3. The analysis of relative growth in secondary sexual characters (abdomen width and major chela length) with respect to carapace length, shows that the pre-puberty and puberty ecdysis occur at 15 and 35 mm carapace length respectively, which was also confirmed by the gonad weight, vas deferens in males, and the onset of vitellogencsis in females.
4. A delay between anatomical and functional (i.e. the ability to copulate successfully) maturity was observed in the males. Being larger may be an advantage in intra-sexual competition for mating, but larger males, being more vagile, are also more likely to meet receptive females. The females may mate before their puberty moult and store sperms in their seminal receptacles for when they attain full maturity; this could be adaptive since opportunities of encountering males are few and far between in their adult phase, characterized by their vagile and amphibious habits.     

The muscular system of Musellifer delamarei (Renaud-Mornant, 1968) and other chaetonotidans with implications for the phylogeny and systematization of the Paucitubulatina (Gastrotricha)

We studied comparatively the muscle organization of several gastrotrich species, aiming at shedding some light on the evolutionary relationships among the taxa of the suborder Paucitubulatina. Under confocal laser scanning microscope, the circular muscles were present in the splanchnic position as incomplete circular rings in Musellifer delamarei (Chaetonotidae) and Xenotrichula intermedia (Xenotrichulidae) and as dorsoventral bands in Xenotrichula punctata, Heteroxenotrichula squamosa and Draculiciteria tesselata (Xenotrichulidae); in the somatic position, M. delamarei shares the presence of dorsoventral muscles with all the Xenotrichulidae, in contrast with the remaining Chaetonotidae that lack these muscles. Maximum parsimony analysis of the muscular characters confirmed monophyly of Paucitubulatina and Xenotrichulidae, while the Chaetonotidae was paraphyletic, with the exclusion of Musellifer , which is the most basal genus within the Paucitubulatina. Xenotrichulidae is the sister taxon to Chaetonotidae, which in turn has Polymerurus as the most basal taxon. In general, the results agree with recent phylogenetic inferences based on molecular characters and support the hypothesis that, within Paucitubulatina, dorsoventral muscles are plesiomorphies retained in marine, interstitial, hermaphroditic gastrotrichs. Dorsoventral muscles were subsequently lost during changes in lifestyle and reproduction modality that took place with the invasion of the freshwater environment. This new information prompted us to reconsider the systematization of Chaetonotidae, proposing the establishment of Muselliferidae fam. nov. to include the genera Musellifer and Diuronotus .  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 379–398.     

Cytogenetic Follow-Up in a Case With a Primary Cutaneous Melanoma and Five Metastatic Lesions

Cytogenetic analyses conducted on several cases of melanoma have contributed to the identification of the chromosomal regions where the sequences responsible for malignant transformation and the evolution of this tumor are probably located. With regard to these problems, it is very important to have the possibility to analyze, through the use of cytogenetics, both the primary melanoma and the metastatic lesions from the same patient. We present a case in which the primary melanoma and five different metastases were studied by using cytogenetics. The primary tumor showed an inversion of chromosome 1 where the p36 region, often proposed in literature as the location of a melanoma susceptibility gene, was involved. Three cutaneous and one lymphonodal metastases presented the same nine clonal chromosomal aberrations. In particular, one is a further rearrangement of the marker present in the primary tumor; another is a deletion of the 9p21pter region in which the p16 gene is located. Our results can provide a contribution to the hypothesis of the location of a candidate gene for melanoma in the 1p36 region and can also underscore the role of the 9p21 region in the progression of melanoma.     

A Maize Mutant with an Altered Vascular Pattern

A recessive maize mutant with disrupted seedling developmentwas isolated following transpositional mutagenesis with Mutator.This mutant, initially identified during germination on thebasis of abnormal growth of the scutellar node, was designatedlsn1 (l arge s cutellar n ode). The mutant seedling exhibitsan enlarged primary root with a longitudinal groove and multipleseparate root tips. The mutant root is shorter than normal,because of defective cell elongation, and lacks lateral roots.The mutant plant shows defective leaves and reduced internodeelongation. Histological analyses on primary root, shoot, scutellarnode and juvenile leaves revealed a series of defects, all relatedto an irregular differentiation of vascular elements. In addition,in situ hybridization of mutant leaves demonstrates an abnormalpattern of expression of Knotted-1, a marker of meristem function.The presence of multiple roots fused together can be interpretedas suppression of the negative control responsible for the differentiationof only one root primordium. Therefore, the data obtained onseedlings of lsn1 point to a relationship between meristem activity,vascular differentiation and auxin polar transport, and mayallow the identification of a gene which is active during embryogenesis.Copyright2000 Annals of Botany Company Auxin, defective seedling, maize, meristem activity, vascular differentiation, Zea mays.     

Patterns of PIP gene expression in Populus trichocarpa during recovery from xylem embolism suggest a major role for the PIP1 aquaporin subfamily as moderators of refilling process

Embolism and the refilling of xylem vessels are intrinsic to the ability of plants to handle the transport of water under tension. Although the formation of an embolized vessel is an abiotic process, refilling against the pressure gradient requires biological activity to provide both the energy and the water needed to restore xylem transport capacity. Here, we present an analysis of the dynamics of embolism and refilling in Populus trichocarpa and follow temporal dynamics of co‐occurring changes in expression level of aquaporins. Under mesic conditions, we found that the percent loss of conductance (PLC) varied diurnally by as much as 20%, suggesting a continuous embolism/refilling cycle. An increase in water stress tilted the balance between the two processes and increased the PLC to as much as 80%. Subsequent re‐watering resulted in the reversal of water stress and recovery of PLC to pre‐stress levels. Stem parenchyma cells responded to drought stress with considerable up‐regulation of the PIP1 subfamily of water channels but not the PIP2 subfamily. Even more significant was the finding that PoptrPIP1.1 and PoptrPIP1.3 genes were up‐regulated in response to embolism, but not to water stress, and were down‐regulated after embolism removal, suggesting a local ability of plants to sense an embolism presence.     

Exploring the history of Serapias politisii (Orchidaceae), a narrow endemic on the opposite coasts of the Otranto channel: insights from molecular investigations

Knowledge of genetic spatial structure may provide insights into the causes of population disjunctions in plants. Serapias politisii is a narrow endemic with only a few populations scattered along the opposite coasts of the Otranto strait (southern Adriatic Sea). It was originally considered to be of hybrid origin between S. vomeracea ssp. laxiflora and S. parviflora, a possibility suggested also by a DNA phylogenetic study that grouped Italian and Greek populations in two distinct clades. In this study we have carried out additional plastid DNA sequencing and an AFLP analysis of the three taxa. Whereas the geographical distribution of four plastid DNA haplotypes supports the likelihood of a double hybrid origin or of a plastid capture, AFLP data do not support such a hypothesis, because S. politisii shows several private alleles, some of which are shared by Italian and Greek populations. In light of the floristic specificity of the coasts bordering the Otranto strait, we consider that the present‐day disjunction of S. politisii could have originated either by a long‐distance seed dispersal or by a fragmentation of an old polymorphic population. The pairwise mismatch distribution excludes a recent expansion of the populations examined. In light of recent evidence concerning the Mediterranean Lago‐Mare period and the westward haplotype evolution detected in some Euro‐Mediterranean trees, we argue that fragmentation of a previously continuous population could be an intriguing possibility. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 572–580.